From d81c34eb834fbd7e72a3bf7f5675578f92be5c41 Mon Sep 17 00:00:00 2001
From: Kyle Sayers <kylesayrs@gmail.com>
Date: Mon, 10 Nov 2025 19:00:27 +0000
Subject: [PATCH] add support for frozen dataclasses

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>
---
 src/llmcompressor/pipelines/cache.py        | 29 +++++++++++----------
 tests/llmcompressor/pipelines/test_cache.py | 11 +++++---
 2 files changed, 22 insertions(+), 18 deletions(-)

diff --git a/src/llmcompressor/pipelines/cache.py b/src/llmcompressor/pipelines/cache.py
index ea0d5f254..84dacd294 100644
--- a/src/llmcompressor/pipelines/cache.py
+++ b/src/llmcompressor/pipelines/cache.py
@@ -1,7 +1,7 @@
 import sys
 import warnings
 from collections import defaultdict
-from dataclasses import dataclass, fields, is_dataclass
+from dataclasses import dataclass, is_dataclass, fields
 from typing import Any, Dict, Generator, List, Optional, Union
 
 import torch
@@ -166,8 +166,8 @@ def _size_helper(intermediate: IntermediateValue) -> int:
                     for v in value.values():
                         _size_helper(v)
                 case _ if is_dataclass(value):
-                    for field in fields(value):
-                        _size_helper(getattr(value, field.name))
+                    for f in fields(value):
+                        _size_helper(getattr(value, f.name))
                 case _:
                     # this handles primitive values that don't match any other cases
                     sizes[torch.device("cpu")] += sys.getsizeof(value, 0)
@@ -211,10 +211,10 @@ def _onload_value(cls, intermediate: IntermediateValue) -> Any:
             case dict():
                 return {k: cls._onload_value(v) for k, v in value.items()}
             case _ if is_dataclass(value):
-                for field in fields(value):
-                    v = getattr(value, field.name)
-                    setattr(value, field.name, cls._onload_value(v))
-                return value
+                return type(value)(**{
+                    f.name: cls._onload_value(getattr(value, f.name))
+                    for f in fields(value)
+                })
             case _:
                 # handles primitive values that should be returned as is.
                 # without this, a MatchError would be raised for unhandled types.
@@ -255,16 +255,17 @@ def _offload_value(
                 )
             case dict():
                 return IntermediateValue(
-                    value={
-                        k: cls._offload_value(v, **kwargs) for k, v in value.items()
-                    },
+                    value={k: cls._offload_value(v, **kwargs) for k, v in value.items()},
                     device=None,
                 )
             case _ if is_dataclass(value):
-                for field in fields(value):
-                    v = getattr(value, field.name)
-                    setattr(value, field.name, cls._offload_value(v, **kwargs))
-                return IntermediateValue(value=value, device=None)
+                return IntermediateValue(
+                    value=type(value)(**{
+                        f.name: cls._offload_value(getattr(value, f.name), **kwargs)
+                        for f in fields(value)
+                    }),
+                    device=None
+                )
             case _:
                 # handles primitive values and provides a warning for unsupported types.
                 # without this, values trigger a MatchError exception.
diff --git a/tests/llmcompressor/pipelines/test_cache.py b/tests/llmcompressor/pipelines/test_cache.py
index 2c5315e18..92fb36466 100644
--- a/tests/llmcompressor/pipelines/test_cache.py
+++ b/tests/llmcompressor/pipelines/test_cache.py
@@ -1,3 +1,5 @@
+from typing import Optional
+
 from dataclasses import dataclass, fields, is_dataclass
 
 import pytest
@@ -7,10 +9,11 @@
 from llmcompressor.pipelines.cache import IntermediatesCache
 
 
-@dataclass
+@dataclass(frozen=True)
 class SampleDataclass:
-    a: torch.Tensor
-    b: int
+    a: int
+    b: Optional[torch.Tensor] = None 
+    c: Optional["SampleDataclass"] = None
 
 
 @pytest.fixture
@@ -36,7 +39,7 @@ def sample_cache(sample_dataloader):
 
 values_to_test = [
     torch.randn(2, 3).to("cpu"),
-    SampleDataclass(a=torch.randn(2, 3), b=42),
+    SampleDataclass(a=42, b=torch.randn(2, 3), c=SampleDataclass(a=64)),
     torch.float32,
     [1, 2, 3],
 ]